i) Field of the Invention
This invention relates to a method and apparatus for vacuum arc deposition of carbon on a substrate; more especially it relates to cathodic arc carbon ion sources typically used in Arc Ion Plating (AIP) devices, to produce diamondlike protective coatings.
ii) Description of Prior Art
Cathodic arc carbon ion sources are typically used in Arc Ion Plating (AIP) devices to produce diamondlike protective coatings. Diamondlike refers to an amorphous form of carbon with properties similar to diamond protective coatings. In AIP devices, an electric arc burning in a vacuum on a graphite cathode generates very small hot spots called "cathode spots", these spots being the site of a strong plasma flux which is directed towards the surface of a substrate to be coated. In addition to the carbon ions present in the plasma flux, these sources also generate small graphite particles typically 0.1-10 .mu.m in diameter, which are deposited with the amorphous carbon film, thereby strongly degrading the coating properties. The small graphite particles are typically formed as a spray of liquid droplets and chunks or irregular non-sperical particles of graphite emitted through thermal shock effects. Preventing these particles from reaching the substrate to be coated is necessary.
Present solutions use various types of filters to eliminate the particle flux between the source and the substrate to be coated. Such filters modify the path of the plasma flux beam, for example, by setting a non-linear or curved ion path by the use of magnetic and/or electric fields. Most particles do not follow the curved path and are collected on the side walls of the vacuum chamber leaving a relatively clean beam arriving at the substrate. Shortcomings of the filters are:
a) a decrease in the output plasma flux and hence in deposition rate and system efficiency; PA1 b) a decrease in the area covered by the beam resulting in smaller surface areas being coated in a given time interval; PA1 c) such systems add to the complexity of the source by imposing a particular source geometry and more importantly an added control of the magnetic/electric field parameters within the filter to be adjusted to the arc source parameters; PA1 d) particles produced by the arc source accumulate in the filter and potentially affect the filter efficiency while imposing shutdown for maintenance in industrial operations; and PA1 e) a portion of the particle flux may still escape into the coating chamber. PA1 low pore size PA1 high density PA1 large grain size PA1 low electrical resistivity (high thermal conductivity).
The AIP coating systems are currently and widely used industrially, for example, to produce the gold colored titanium nitride films in medical implants, in the automotive industry, decorative industry, and for more resistant cutting tools. In such systems, particles are emitted typically in a smaller quantity compared to carbon sources and the resulting coating degradation has generally been considered not detrimental for most applications. Simple multi-source coating chambers are generally being used industrially to produce these coatings. In an industrial environment, the complexity of the filtered source geometry strongly restrains the transfer from a multi-source AIP chamber device to the deposition of diamondlike. A specific deposition setup is needed for diamondlike, while the multi-source deposition chambers can accommodate various types of coatings by changing the cathode material in the source.